/*
 * Licensed to the Apache Software Foundation (ASF) under one or more
 * contributor license agreements.  See the NOTICE file distributed with
 * this work for additional information regarding copyright ownership.
 * The ASF licenses this file to You under the Apache License, Version 2.0
 * (the "License"); you may not use this file except in compliance with
 * the License.  You may obtain a copy of the License at
 * 
 *  http://www.apache.org/licenses/LICENSE-2.0
 * 
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package com.mlizhi.base.codec.binary;

import java.io.FilterInputStream;
import java.io.IOException;
import java.io.InputStream;

/**
 * Provides Base64 encoding and decoding in a streaming fashion (unlimited size). When encoding the default lineLength
 * is 76 characters and the default lineEnding is CRLF, but these can be overridden by using the appropriate
 * constructor.
 * <p>
 * The default behaviour of the Base64InputStream is to DECODE, whereas the default behaviour of the Base64OutputStream
 * is to ENCODE, but this behaviour can be overridden by using a different constructor.
 * </p>
 * <p>
 * This class implements section <cite>6.8. Base64 Content-Transfer-Encoding</cite> from RFC 2045 <cite>Multipurpose
 * Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies</cite> by Freed and Borenstein.
 * </p>
 * <p>
 * Since this class operates directly on byte streams, and not character streams, it is hard-coded to only encode/decode
 * character encodings which are compatible with the lower 127 ASCII chart (ISO-8859-1, Windows-1252, UTF-8, etc).
 * </p>
 * 
 * @author Apache Software Foundation 
 * @version $Id: Base64InputStream.java 799805 2009-08-01 04:33:05Z ggregory $
 * @see <a href="http://www.ietf.org/rfc/rfc2045.txt">RFC 2045</a>
 * @since 1.4
 */
public class Base64InputStream extends FilterInputStream {

private final boolean doEncode;

private final Base64 base64;

private final byte[] singleByte = new byte[1];

/**
 * Creates a Base64InputStream such that all data read is Base64-decoded from the original provided InputStream.
 * 
 * @param in
 *InputStream to wrap.
 */
public Base64InputStream(InputStream in) {
this(in, false);
}

/**
 * Creates a Base64InputStream such that all data read is either Base64-encoded or Base64-decoded from the original
 * provided InputStream.
 * 
 * @param in
 *InputStream to wrap.
 * @param doEncode
 *true if we should encode all data read from us, false if we should decode.
 */
public Base64InputStream(InputStream in, boolean doEncode) {
super(in);
this.doEncode = doEncode;
this.base64 = new Base64();
}

/**
 * Creates a Base64InputStream such that all data read is either Base64-encoded or Base64-decoded from the original
 * provided InputStream.
 * 
 * @param in
 *InputStream to wrap.
 * @param doEncode
 *true if we should encode all data read from us, false if we should decode.
 * @param lineLength
 *If doEncode is true, each line of encoded data will contain lineLength characters (rounded down to
 *nearest multiple of 4). If lineLength <=0, the encoded data is not divided into lines. If doEncode is
 *false, lineLength is ignored.
 * @param lineSeparator
 *If doEncode is true, each line of encoded data will be terminated with this byte sequence (e.g. \r\n).
 *If lineLength <= 0, the lineSeparator is not used. If doEncode is false lineSeparator is ignored.
 */
public Base64InputStream(InputStream in, boolean doEncode, int lineLength, byte[] lineSeparator) {
super(in);
this.doEncode = doEncode;
this.base64 = new Base64(lineLength, lineSeparator);
}

/**
 * Reads one <code>byte</code> from this input stream.
 * 
 * @return the byte as an integer in the range 0 to 255. Returns -1 if EOF has been reached.
 * @throws java.io.IOException
 * if an I/O error occurs.
 */
public int read() throws IOException {
int r = read(singleByte, 0, 1);
while (r == 0) {
r = read(singleByte, 0, 1);
}
if (r > 0) {
return singleByte[0] < 0 ? 256 + singleByte[0] : singleByte[0];
}
return -1;
}

/**
 * Attempts to read <code>len</code> bytes into the specified <code>b</code> array starting at <code>offset</code>
 * from this InputStream.
 * 
 * @param b
 *destination byte array
 * @param offset
 *where to start writing the bytes
 * @param len
 *maximum number of bytes to read
 * 
 * @return number of bytes read
 * @throws java.io.IOException
 * if an I/O error occurs.
 * @throws NullPointerException
 * if the byte array parameter is null
 * @throws IndexOutOfBoundsException
 * if offset, len or buffer size are invalid
 */
public int read(byte b[], int offset, int len) throws IOException {
if (b == null) {
throw new NullPointerException();
} else if (offset < 0 || len < 0) {
throw new IndexOutOfBoundsException();
} else if (offset > b.length || offset + len > b.length) {
throw new IndexOutOfBoundsException();
} else if (len == 0) {
return 0;
} else {
if (!base64.hasData()) {
byte[] buf = new byte[doEncode ? 4096 : 8192];
int c = in.read(buf);
// A little optimization to avoid System.arraycopy()
// when possible.
if (c > 0 && b.length == len) {
base64.setInitialBuffer(b, offset, len);
}
if (doEncode) {
base64.encode(buf, 0, c);
} else {
base64.decode(buf, 0, c);
}
}
return base64.readResults(b, offset, len);
}
}

/**
 * {@inheritDoc}
 * 
 * @return false
 */
public boolean markSupported() {
return false; // not an easy job to support marks
}
}
